How rat poison normally used to kill rats ended up in "a gift" of sandwiches for 25 auto workers in Germany remains unclear. (Photo: Creative Commons)

Poisoned bread - specifically rolls infested with rat poison - sent 25 auto parts workers in Germany to the hospital on Tuesday, according to reports.

UPI reported that the poisoned bread was part of sandwiches consumed by the workers of Muller Technology, a manufacturing and engineering firm in Steinfeld, Lower Saxony. The sandwiches were left on the doorstep Tuesday morning in two plastic containers, with a note saying that they were sent as "a gift."

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The workers helped themselves to the poisoned bread until one worker noticed that there was an unusual substance on the rolls and called police. As a result, everyone who dug in went to the hospital, while the leftover rolls were flown by helicopter to a specialist laboratory in Berlin for testing as the BBC noted.

Tests carried out on the poisoned bread overnight confirmed the presence of rat poison. Investigators said that the poisoned bread contained unusual red grains, but apparently no one suspected anything could be wrong until after office workers had consumed the rolls.

As of Wednesday, none of those hospitalized had shown symptoms of poisoning, but are still being kept under observation as a precautionary measure, said police spokesman Frank Soika.

"We don't believe the amount of poison used would have been deadly, but it could have caused serious illness," said Soika.

Police said there were no suspects and the motive for the poisoning remains unknown.